Astrophysical Distance Scale The JAGB Method: I. Calibration and a First Application

Understand

J-Branch Asymptotic Giant Branch (JAGB) stars are a photometrically well-defined population of extremely red, intermediate-age AGB stars that are found to have tightly-constrained luminosities in the near-infrared.

• Based on JK photometry of some 3,300 JAGB stars in the bar of the Large Magellanic Cloud (LMC) we find that these very red AGB stars have a constant absolute magnitude of <M_J> = -6.22 mag, adopting the Detached Eclipsing Binary (DEB) distance to the LMC of 18.477 +/- 0.004 (stat) +/- 0.026 (sys).
• Undertaking a second, independent calibration in the SMC, which also has a DEB geometric distance, we find <M_J> = -6.18 +/- $ 0.01 (stat) +/- 0.05~(sys) mag.
• The scatter is +/-0.27 mag for single-epoch observations, (falling to +/-0.15~mag for multiple observations averaged over a window of more than one year).